What is the sum of the solutions of the equation x2+8x+15=0

I assume that what you meant to ask is the sum of the solutions for:


x^2 + 8x + 15 = 0


First step is to factor the equation into the form (x+a)(x+b) =0. I won't do this for you, but you need to find two numbers that when multiplied together give 15, and when added together give 8. From this the two solutions are -a and -b. Add them up to get the answer. Hope this helps get you started.

5+2
8+3
11

Hi at my school we never learned this so I don't know what to do. I'm trying to learn so I can know what to do in the future.

when you expand (x+a)(x+b) you get x^2+ax+bx+ab = x^2+(a+b)x+ab

Comparing this to your question, we see that a and b need to be 2 numbers such that their sum is 8 and their product is 15.

Can you find the 2 numbers that fit this?

when you expand (x+a)(x+b) you get x^2+ax+bx+ab = x^2+(a+b)x+ab

Comparing this to your question, we see that a and b need to be 2 numbers such that their sum is 8 and their product is 15.

Can you find the 2 numbers that fit this?

Ah, good! Capuchin showed up. He can help to show you how to solve problems on your own so that you aren't always looking for people on this site to answer them for you.

Then, once you find a and b (should be quite easy), you can see from (x+a)(x+b) = 0 that the solutions are where x = -a and x = -b (ie where (x+a)=0 or (x+b)=0).

There's your 2 solutions! You just did it! :)

You should now have plenty of information to find the answer to this, and any other quadratic question where the coefficient of x^2 is 1.

Good luck!