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Re: If 4^(2X + 1) + 4^(X+1) = 80. Find value of X
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06 Nov 2014, 22:21

1

If 4^(2X + 1) + 4^(X+1) = 80. Find value of X :

We can rewrite the equation: 4*(4^(2x)+4^(x))=4^(2)*5 => 4^(2x)+4^(x)=4*5. Let 4^(x)=y, and we have y^(2)+y=20 or (y-4)(y+5)=0 therefor y=4 or y=-5. Let take y=4, and we have 4^(x)=4^(1) => x=1. The answer is C.

Re: If 4^(2X + 1) + 4^(X+1) = 80. Find value of X
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08 Mar 2016, 08:05

Serje wrote:

If 4^(2X + 1) + 4^(X+1) = 80. Find value of X :

We can rewrite the equation: 4*(4^(2x)+4^(x))=4^(2)*5 => 4^(2x)+4^(x)=4*5. Let 4^(x)=y, and we have y^(2)+y=20 or (y-4)(y+5)=0 therefor y=4 or y=-5. Let take y=4, and we have 4^(x)=4^(1) => x=1. The answer is C.

I did it the same way ...But here i this we can use the options to check the sides ....That actually is easy here.
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