SOLUTION: Hi! I have a homework that says: solve the following quadratic equations by factoring. a) x^2+8x+7=0 I tried to solve it and I got this answer (x+1) (x+7)=0. b) 2y^2 + 12

Question 596729: Hi!
I have a homework that says:
solve the following quadratic equations by factoring.
a) x^2+8x+7=0 I tried to solve it and I got this answer (x+1) (x+7)=0.
b) 2y^2 + 12y +10=0 I got: 2(y^2+6y+5)=0
c) x^2=81 I'm not sure how o solve this one.
However the =0 confuses me do I have to use the quadratic formula to solve them?
Thank you.
Answer by KMST(5328) (Show Source): You can put this solution on YOUR website!
I would not use the quadratic formula unless I really had to, and the instructions say to use factoring.

a) You factored the quadratic polynomial to get .
For the product to be zero, one factor must be zero.
gives you one solution:
gives you the other solution:

b) You factored the quadratic polynomial to get
Factoring a little further, you get
One of those factors must be zero.
gives you one solution:
gives you the other solution:

c) is easy, except for the question of using factoring.
means that x is a number that squared equals 81.
You know one such number: and is one solution.
There is also because too.
Maybe you were expected to transform it by subtracting 81 from both sides to get
and then factor to get .
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