Question: Power with Binomial Product

Comment on Power with Binomial Product

Could you please explain why it was not possible to factor the quadratic equation in the conventional method? I did factor it, and I got (x+2) (x-1)=0. So, X=-2 or X=1. When I substitute both values in (A), I get -12 and -10, both of which are lesser than option (B).
greenlight-admin's picture

Your factoring is not quite right.
When we expand (x+2)(x-1), we get x^2 + x - 2 (not x^2 + x - 3)

(x+4)(x-3)=x^2-3x+4x-12
=x^2+x-12
add +9 to both sides we end up with
x^2+x-3 0
16^(x^2+x-3) 16^0
1 1
answer is c
greenlight-admin's picture

Great!

That was tricky.
greenlight-admin's picture

Indeed!

Great question. It's interesting how sometimes the tricky ones you can get straight away (as I just did), and some more straight forward ones I can't see the right path to take. Thanks!

I hope this kind of question will not appear in test day! Can be time consuming.
greenlight-admin's picture

It's definitely a tricky one!!

If x^2+x-3 = (x-3)(x+1) = 0 therefore x = 3,-1
then place x either 3 or -1 to (x+4)(x-3) i got QA = 0 or -12 so why i cannot answer D
greenlight-admin's picture

Be careful. x²+x-3 does not equal (x-3)(x+1)

If we take (x-3)(x+1) and expand it (using the FOIL method), we get: x²-2x-3 (not x²+x-3)

As mentioned in the video, we cannot factor the expression x²+x-3

Cheers,
Brent

These Quantitative comparisons questions are really giving me a tough time. It's hard to know when to ignore the expression given above and focus on the Quantities. They're somw questions you solved without touching the expression that preceds the Quantities while some depended on the Quantities. I need a link to more practice questions
greenlight-admin's picture

You're right; sometimes we need to use the given information immediately, and sometimes we use the given information later on.

Whether you use the given information at the beginning of the solution or near the end will depend on the nature of the question.

This scenario plays out in most Quantitative Comparison questions, which you'll find links to throughout the course (in the Reinforcement Activities boxes)

Cheers,
Brent

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