Year 12s: what will be the first way you research your future options? >>

Year 12s: what will be the first way you research your future options? >>

Year 12s: what will be the first way you research your future options? >>

Solomon paper A c3 question

Lilly1234567890

The tangent to the curve y=2xtanx at the point where x=Pi/4 meets the y-axis at the point P.

(b) Find the y-coordinate of P in the form kPi^2 where K is a rational constant.

This was my working out:

dy/dx= 2xsec^x+2tanx
m=2+pi

y=(2+pi)x+c

I got everything correct so far. However, when I try to find C something goes wrong and I just cant see it.

pi/2=2pi/4+pi^2/4+c

c= -pi^2

y=-1pi^2

But that is wrong and the answer is -1/4pi^2

Thanks in advance !

Original post by Lilly1234567890

pi/2=2pi/4+pi^2/4+c

c= -pi^2

Here's your mistake. Have a look at it again and if you get the same thing, try to explain why you think it's -pi^2.

Lilly1234567890

OP

Original post by notnek

Here's your mistake. Have a look at it again and if you get the same thing, try to explain why you think it's -pi^2.

I was thinking that if:

pi/2=2pi/4+pi^2/4+c
Then you can multiply everything by 4:
2pi=2pi+pi^2 +c
so c= -pi^2

I'm still getting that answer.

Original post by Lilly1234567890

I was thinking that if:

pi/2=2pi/4+pi^2/4+c
Then you can multiply everything by 4:
2pi=2pi+pi^2 + 1c
so c= -pi^2

I'm still getting that answer.

You haven't multiplied everything by 4...

Lilly1234567890

OP

Original post by Zacken

You haven't multiplied everything by 4...

OMG thanks so much !! I didn't even notice that.

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