If y 2x 1 x7 3 What is y Solutiony 2x1x73 Let y uv3 y 3u
If y = (2x- 1 / x+7 )^3. What is y\' ?
Solution
y= (2x-1)/(x+7)^3
Let y= (u/v)^3
==> y\' = 3*(u/v)\' (u/v)^2
But (u/v)\' = (u\'v-uv\')/v^2
==> y\' = 3*[(u\'v-uv\')/v^2] *(u/v^2)
= 3*[uu\'v - u^2*v]/v^4
u= 2x-1 ==> u\' = 2
v= x+7 ==> v\' = 1
Now substitute:
==> y\' = 3[2(2x-1)(x+7) - (2x-1)^2 ]/(x+7)^4
= 6(2x^2+13x -7) - (4x^2 -4x + 1)]/(x+7)^4
= (12x^2 + 78x - 42 - 4x^2 + 4x -1)/(x+7)^4
= (8x^2 +82x - 43)/(x+7)^4
==> y\' = (8x^2 + 82x - 43)/(x+7)^4

