Need help

Hi Htown,

Welcome to the forum :)

what plus what = 7 and what times what = -8 only using two numbers

Look at the times first.

The two numbers mult multiply to a negative number - so one will be positive and the other negative.

Mmm

They also have to add to a positive so the bigger one of the two numbers will be the positive one

They times to 8 so

-1 * +8   = - 8

-2 *  +4  =  -8

They are the only two choices so far (sincethe big one has to be the positive one)

-1+8=7

-2+4=2

So the numbers have to be     -1 and +8

Let me know if that helps :)

If you know how use the X-Box method, its specifficaly made for problems like that. Hope it works!!!

a+b=7  

a*b =-8

a=8, b=-1

b=8, a=-1

what plus what = 7 and what times what = -8 only using two numbers

\(\begin{array}{|rclcl|} \hline x^2+p \cdot x + q &=& 0 \qquad | \qquad -p=(x_1+x_2) & & q = x_1\cdot x_2 \\ x^2 -7 x -8 &=& 0 \qquad | \qquad -p=7 & & q =-8 \\\\ x_{1,2} &=& \frac{7\pm \sqrt{49-4\cdot(-8)} }{2} \\ x_{1,2} &=& \frac{7\pm \sqrt{81} }{2} \\ x_{1,2} &=& \frac{7\pm 9 }{2} \\\\ x_1 &=& \frac{7 + 9 }{2} \\ \mathbf{x_1} &\mathbf{=}& \mathbf{8} \\\\ x_2 &=& \frac{7 - 9 }{2} \\ \mathbf{x_2} &\mathbf{=}& \mathbf{-1} \\ \hline \end{array}\)

8-1 = 7
8*(-1) = -8