SOLUTION: If 4a^2-10ab-6b^2=20 and 2a+b=2 , 3a-9b is equal to what?

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Question 1082030: If 4a^2-10ab-6b^2=20 and 2a+b=2 , 3a-9b is equal to what?
Found 2 solutions by solver91311, ikleyn:
Answer by solver91311(24713) About Me  (Show Source):
You can put this solution on YOUR website!














John

My calculator said it, I believe it, that settles it

Answer by ikleyn(52800) About Me  (Show Source):
You can put this solution on YOUR website!
.
We are given

4a%5E2-10ab-6b%5E2 = 20        (1)
2a + b = 2.              (2)

Square equation (2). You will get

4a%5E2+%2B+4ab+%2B+b%5E2 = 4.         (3)

Subtract (3) from (1). Yu will get

-14ab+-+7b%5E2 = 16.         (4)

Simplify (4):

(-7b)*(2a + b) = 16.     (5)

In (5), replace (2a + b) by 2, according to (2). You will get

(-7b)*(2) = 16,

which implies   b = -8%2F7.


From this point please complete the solution on your own.

Solved.