Given that y = sin 3x + cos^3 x, find the value of dy/dx when x = pi/6. If x increases at a constant rate of 0.3 radians per second, find the rate of change of y when x = pi/6.
Need help with only the first part(you can do the 2nd one if you please ;D)
I got -2.68 and but the given answer is -9/8. I am pretty sure this is correct, or so I think. -9/8 is the answer when you differentiate cos^3 x.
So yea, help me out! Millions thanks.
I got -1.06 which is somewhere near -9/8 using handphone and mental sums.
Ok, careless mistake. I got -9/8 exactly.
Add-on: You should get dy/dx = -3sin x cos ^2 x + 3cos 3x
dy/dx = 3 cos3x + (3)(cos^2 x)(-sinx)
calculator set in degree mode when x = 30
subst. into dy/dx, answer = -9/8
If your dy/dx is the same as mine. then it would be your calculator skill.
Shouldn't it be in radian mode? My answer's in radians. So it should be correct when I convert to degree.
Originally posted by anpanman:Shouldn't it be in radian mode? My answer's in radians. So it should be correct when I convert to degree.
If calculator is rad mode then use x=pi/6......if calculator is deg mode then use x=30.
anpanman seems determined to get an A1 and he is sure to get it. Gratz in advance for your 2 A1s in E Maths and A Maths.
People don't seem to realise that efforts spent on A Maths is the most worth it one. Practise A Maths and your E Maths plus Physics got benefit also.
Agreed
There's quite an amount of algebra required in Physics
And when you go to A lvl physics (or uni), you need even more maths