The gradient (usually referred to as the slope) of a line indicates its steepness. There is an equation that allows one to calculate the gradient. It is the following:
\(m=\frac{y_2-y_1}{x_2-x_1}\)
m = slope of line
Before we can understand this equation, let's try putting it to use on some lines:
Source: http://www.coolmath.com/sites/cmat/files/images/06-lines-01.gif
Let's use this line and the points designated on the line to figure out its slope:
\(m=\frac{y_2-y_1}{x_2-x_1}\) | Plug in the appropriate value for the y-coordinates and the x-coordinates. |
\(m=\frac{3-(-1)}{4-(-2)}\) | Simplify the numerator and denominator by recognizing that subtracting a negative is equivalent to adding a positive. |
\(m=\frac{3+1}{4+2}\) | |
\(m=\frac{4}{6}\) | When finding the gradient, you should simplify it into simplest terms |
\(m=\frac{2}{3}\) | |
It does not matter which order you subtract the y-coordinates, but make sure that you subtract them in the same order as your x-coordinates. Otherwise, your slope will be incorrect.
I am assuming that you want this equation solved using the quadratic formula. I would use that method, too. Of course, let's remind ourselves of the quadratic formula:
In a quadratic function in the form \(ax^2+bx+c=0\).
\(x = {-b \pm \sqrt{b^2-4ac} \over 2a}\)
The question, however, asks for how much time elapsed when it (I assume a thrown ball) reached a height of 3 meters
\(3=-5t^2+8t+1.3\) | Subtract 3 on both sides. |
\(0=-5t^2+8t-1.7\) | |
Now that the equation is in the form of \(ax^2+bx+c=0\), let's solve for how much time, t, it took for it to reach 3 meters:
\(0=-5t^2+8t-1.7\) | Use the quadratic formula to solve for t. | ||
\(t = {-8 \pm \sqrt{8^2-4(-5)(-1.7)} \over 2(-5)}\) | We should first calculate the discriminant \(b^2-4ac\) to see if there are indeed solutions for t. Let's just focus on that part. | ||
\(8^2-4(-5)(-1.7)\) | Do 8^2 first. | ||
\(64-4(-5)(-1.7)\) | Do 4*-5 next. | ||
\(64-(-20)(-1.7)\) | Do -20*-1.7 | ||
\(64-34\) | |||
\(30\) | Because \(b^2-4ac>0\), this means that there are 2 solutions. Replace \(8^2-4(-5)(-1.7)\) with its calculated value, 30. | ||
\(t=\frac{-8\pm\sqrt{30}}{2(-5)}\) | SImplify 2*-5 in the denominator | ||
\(t=\frac{-8\pm\sqrt{30}}{-10}\) | Break up the fraction by doing \(\frac{a\pm b}{c}=\frac{a}{c}\pm\frac{b}{c}\) | ||
\(t=\frac{-8}{-10}\pm\frac{\sqrt{30}}{-10}\) | Simplify -8/-10 by realizing its GCF is -2. | ||
\(t=\frac{4}{5}\pm\frac{-\sqrt{30}}{10}\) | Split your answer into two answers | ||
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The question asks for the first time that the ball hits 3 meters. Of course, we do not know the exact value of either of our solutions currently. We can utilize logical thinking to figure it out, however.
If we pretend as if \(\sqrt{30}=5\), as that is an OK approximation, we can simplify both solutions into
\(t=\frac{4}{5}-\frac{1}{2}\) and \(t=\frac{4}{5}+\frac{1}{2}\)
We can infer that \(\frac{4}{5}-\frac{1}{2}\) is still positive but closer to 0 because 4/5 is greater than 1/2. Subtracting the two would make it closer to 0. Adding both would make the numbers further from 0.
Therefore, the first time it goes to the height of 3 meters is after \(\frac{4}{5}-\frac{\sqrt{30}}{10}\) that much time elapsed. \(\frac{4}{5}-\frac{\sqrt{30}}{10}\approx0.252277\).
I have supllied a link to a graph if ou would like to check it out: https://www.desmos.com/calculator/ivnsia7gdd
If we think about the expansion of a binomial of a big power (like 7). The expansion looks like the following:
\((a+b)^n={n\choose 0}a^nb^0+{n\choose 1}a^{n-1}b^1+...+{n\choose n}a^0b^n\)
Knowing that this pattern exists, let's utilize that in the current expansion of the expression:
\((2x+3)^7={7\choose0}(2x)^7(3)^0+{7\choose1}(2x)^6(3)^1+{7\choose2}(2x)^5(3)^2+{7\choose3}(2x)^4(3)^3+{7\choose4}(2x)^3(3)^4+...\)
Why don't I care about the other terms? Well, I only care about the terms that has the x^5. If it doesn't have that, then I can ignore that term. In this case the appropriate term is \({7\choose 2}(2x)^5(3)^2\). Let's evaluate it:
\({7\choose 2}(2x)^5(3)^2\) | First, let's evaluate the function that has the 7 choose 2. This has a formula to it. |
The formula for the choose function is the following:
\({x \choose y}=\frac{x!}{y!(x-y)!}\)
Let's apply that to \({7\choose 2}\) first:
\(7\choose2\) | Apply the formula to figure out its true value |
\(\frac{7!}{2!(7-2)!}\) | |
\(\frac{7!}{2!*5!}\) | Let's expand the factorial function. |
\(\frac{7*6*5*4*3*2*1}{2*1*5*4*3*2*1}\) | It is very obvious that there is a common factor of 5! in both the numerator and denominator, so let's factor that out. |
\(\frac{7*6}{2}\) | Simplify the numerator completely. |
\(\frac{42}{2}=21\) | |
Ok, now let's continue with our problem:
\({7\choose 2}(2x)^5(3)^2\) | Replace \({7\choose 2}\) with its calculated value, 21. |
\(21*(2x)^5*3^2\) | Distribute the power to the 5 to 2 and the x |
\(21*2^5x^5*3^2\) | Simplify all the constants. |
\(21*32*x^5*9\) | Do the multiplication of all the constants. |
\(6048x^5\) | |
Therefore, the coefficient in front of the x^5 is 6048.
To do this problem, evaluate n at the values from the positive integers n=3 to n=7
When n=3:
\(2n+3\) | Plug in the appropriate value for n, which is 3, in this case. |
\(2*3+3\) | |
\(6+3\) | |
\(9\) | |
Now, let's evaluate it for n=4:
\(2n+3\) | Plug in n=4 |
\(2*4+3\) | |
\(8+3\) | |
\(11\) | |
n=5:
\(2n+3\) | Replace all instances of n with 5 |
\(2*5+3\) | |
\(10+3\) | |
\(13\) | |
n=6:
\(2n+3\) | Plug in 6 for n |
\(2*6+3\) | |
\(12+3\) | |
\(15\) | |
Now, I do not have to evaluate 7 as I can infer, based on the information above, that the next value in the series will be the sum of the last number in the series and 2. Therefore, 2n+3 when n=7, the expression evaluates to 17.
Now, our last step is too add the series together:
\(9+11+13+15+17\) | Figure out what this evaluates to. Of course, with addition you can add in whatever order you'd like. I'll use this property to my advantage to ease calculation. |
\(20+13+15+17\) | |
\(20+30+15\) | |
\(50+15\) | |
\(65\) | |