Solve: 16x2 − 81 = 0.
x = 4, 9
x = −4, −9
x = 9 over 4, x = −9 over 4
x = 81 over 16, x = −81 over 16

Question

Solve: 16x2 − 81 = 0.
x = 4, 9
x = −4, −9
x = 9 over 4, x = −9 over 4
x = 81 over 16, x = −81 over 16

anonymous · Answer

@welshfella

welshfella · Answer

note that 16x^2 and 81  are 2 perfect squares
so what are the factors of 16x^2 - 81?

welshfella · Answer

this is the difference of 2 squares 

a^2 - b^2 = (a + b)(a - b)

anonymous · Answer

I do believe the answer is D.

welshfella · Answer

try to factor the expression

compare  16x^2 - 81 with a^2 - b^2   and plug the values in

anonymous · Answer

16^12-81^2?

welshfella · Answer

what are the square roots of 16x^2 and 81?

welshfella · Answer

no a and b are the square roots of 16x^2 and 81

anonymous · Answer

I think the answer is D. Am i correct?

welshfella · Answer

no

welshfella · Answer

what number multiplied by itself = 81?

anonymous · Answer

The answer I belive it is @welshfella make sure I am correct on this lol. B.

anonymous · Answer

@welshfella is she correct?

welshfella · Answer

no its not d

the important thing is you learn how to solve this

anonymous · Answer

ok

welshfella · Answer

ok lets do it another way
16x^2 - 81 = 0
add 81 to both sides
16x^2 = 81

now divide both sides by 16 

what do you get?

anonymous · Answer

I am confused.

welshfella · Answer

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