Select the approximate values of x that are solutions to f(x)=0, where f(x)=-8x^2+8x+7

a.(1.56,-0.56)

b.(-8,8)

c.(-1.00,-0.88)

d.(-1.14,1.14)

Select the approximate values of x that are solutions to f(x)=0, where f(x)=-8x^2+8x+7

a.(1.56,-0.56)

b.(-8,8)

c.(-1.00,-0.88)

d.(-1.14,1.14)

Tutors, please sign in to answer this question.

Tarzana, CA

This is a multiple-choice question - the type you find on standardized tests like the SAT. Your approach should be to answer the question as quickly as possible without worrying about understanding details.

Rule #1: On a multiple-choice question, your first step is not to work the problem.

The first step is to eliminate as many answers as possible, and in this case it's sufficient.

The answer is (a) for the following reasons:

1.56 squared is about 2.5, so the expression is close to zero.. 1.56 definitely a candidate

-8 , -1 and -1.14 don't come close to making the expression zero. - do a rough estimate in your head.

So the only possible answer is a because for the other choices one solution definitely fails.

Remember, on a standardised test (or any multiple-choice question like this) your goal is to select the right answer, and not to prove you can work the problem! Just select the right answer, then go on to the next problem!

Never take any problem personally on a standardized test - for example, if you feel shaky about your ability to work a problem - don't let that enter into the equation. Just use what you know.

This approach works really well on multiple-choice tests because most test-writers are lazy and don't take time or don't know how to make up credible alternative answers.

Rule #1: On a multiple-choice question, your first step is not to work the problem.

The first step is to eliminate as many answers as possible, and in this case it's sufficient.

The answer is (a) for the following reasons:

1.56 squared is about 2.5, so the expression is close to zero.. 1.56 definitely a candidate

-8 , -1 and -1.14 don't come close to making the expression zero. - do a rough estimate in your head.

So the only possible answer is a because for the other choices one solution definitely fails.

Remember, on a standardised test (or any multiple-choice question like this) your goal is to select the right answer, and not to prove you can work the problem! Just select the right answer, then go on to the next problem!

Never take any problem personally on a standardized test - for example, if you feel shaky about your ability to work a problem - don't let that enter into the equation. Just use what you know.

This approach works really well on multiple-choice tests because most test-writers are lazy and don't take time or don't know how to make up credible alternative answers.

Westford, MA

f(x) = -8x^2 + 8x + 7 = 0

8x^2 - 8x - 7 = 0

(ax + b)^2 = (ax)^2 + 2abx + b^2

(x√(8))^2+2(√(8))(-√(8)/2)x+(-√(8)/2)^2-(-√(8)/2)^2-7=0

(x√(8)-√(8)/2)^2 - (-√(8)/2)^2 - 7 = 0

8(x-1/2)^2 - (8/4) - 7 = 0

8(x-1/2)^2 = 9

(x-1/2)^2 = 9/8 = 3*3*2/2*2*2*2

|x-1/2| = 3√(2)/4

x = 1/2 ± 3√(2)/4

The only answer with pairs whose average is 1/2 is A.

Dana R.

English/Math SAT PrepTutor with PhD

Lynbrook, NY

4.8
(85 ratings)

John Y.

Columbia Math and SAT Specialist

New York, NY

5.0
(315 ratings)

Dr. Anthon S.

Best Results By Perfect Score SAT/ACT Tutor! Math, Physics and more!

New York, NY

5.0
(456 ratings)

- Odd Functions 1
- Math Help 4833
- Algebra 4545
- Math 8560
- Algebra 2 3144
- Algebra 1 3721
- Function 188
- Word Problem 4708
- Functions Word Problem 77
- Precalculus 1412

## Comments