quick question (1 Viewer)

[Lazy Lankan]

I got a Mathematics 1 mid-semester on Wednesday - and I don't even know how to differentiate - WTF! what am I doing wrong?:

I am supposed to differentiate y = (x^2+1)(x^3+1)

by expanding and differenitiating I get:

dy/dx = 5x^4+2x+3x^2 (which is the right answer)

By product rule (AB'+BA') - I get the wrong answer - what have I done wrong?

dy/dx = (x^2+1)(3x^2)+(x^3+1)(2x)
= 3x^5+3x^2+2x^4+2x

HELP!

 

[shafqat]

dy/dx = (x^2+1)(3x^2)+(x^3+1)(2x)
= 3x^5+3x^2+2x^4+2x

try expanding again

 

[Lazy Lankan]

oops!

dy/dx = (x^2+1)(3x^2)+(x^3+1)(2x)
= 3x^4+3x^2+2x^4+2x

But I still get the wrong answer!

 

[velox]

dy/dx = (2x)(x^3+1) + (x^2+1)(3x^2)
= 2x^4 + 2x + 3x^4 + 3x^2
= 5x^4 + 3x^2 + 2x

 

[velox]

No lazy lankan thats right. Add the x^4 up.

 

[Lazy Lankan]

Hahahahahahaha

Omg

Sorry! I Feel Like An Idiot - Add Common Variables !!!

 

[Lazy Lankan]

THANX ... what a stupid mistake?! who would have known that I did 3 unit maths in yr 12 and actually got a band e4 *hangs head in shame* lol