solve the following a/b/c/or d

Question

(6/y+5)-(9/y-5)=(15/y^2-25)

a -30

b 90

c 64

d 30

Answer 1

(6/y+5)-(9/y-5)=(15/y^2-25)  remember y^2 - 25 is equal to (y - 5)(y + 5).  so multiply by the factors

6(y - 5) - 9(y + 5) = 15

6y - 30 -9y - 45 = 15

-3y = 90

y = 30

answer is d...

Answer 2

The easiest way to find the answer, you might think, is to go through each option and substitute for y. You'd eventually find out which option is right! Unfortunately, it wouldn't go down well with your tutor or examiner! And you'd lose points, no doubt.

The right side of the equation can be written 15/((y-5)(y+5)). That's the giveaway to solve the equation, because the left side of the equation has these in the fractions. Multiply both sides of the equation by this numerator and we get:

6(y-5)-9(y+5)=15.

The fractions on the left have numerators that divide exactly into the multiplier from the right side of the equation. Open the brackets and we get:

6y-30-9y-45=15.

Opening the second bracket forces - to become +, giving us -45, not +45. Take the numbers over to the right and gather the y's together on the left and we get -3y=90, so y=-30, which is option a.

 

 

 

 

 

 

 

Answer 3

Given (6/(y+5))-(9/(y-5))=(15/(y^2-25))
[6(y-5)-9(y+5)]/(y^2-25)=15/(y^2-25)
6y-30-9y-45=15
-3y=15+45+30
y=-30

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