TheXSquaredFactor

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UsernameTheXSquaredFactor
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Questions 3
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 #2
avatar+2446 
+1

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.

 #1
avatar+2446 
0

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
\(t=\frac{4}{5}+\frac{-\sqrt{30}}{10}\) \(t=\frac{4}{5}-\frac{-\sqrt{30}}{10}\)

 

 
   

 

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

 #1
avatar+2446 
0

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.