# Math Help - general solutions

1. ## general solutions

write a general solution for
cos3x=(-sin2x)

I changed sin to cos and then solved the equation and got the general solution of x = 2npi + (pi)/2 OR x= (4npi-pi)/10

Can anyone tell me if this is correct or not?
Much appreciated.

And for this question

y=5sin(3x-pi/4) has maximum and minimum values at?

Well, i said it has max and min values at y=5 and -5 and then i solved the equation
For maximum values, when y=5

I got x = [4npi+(-1)^n(2pi) +pi]/12

I would really really appreciate it if someone could check that for me and tell me if it's right or wrong

THankyou =)

2. Originally Posted by christina
write a general solution for
cos3x=(-sin2x)

I changed sin to cos and then solved the equation and got the general solution of x = 2npi + (pi)/2 OR x= (4npi-pi)/10

Can anyone tell me if this is correct or not? Mr F says: Correct.
Much appreciated.

And for this question

y=5sin(3x-pi/4) has maximum and minimum values at?

Well, i said it has max and min values at y=5 and -5 and then i solved the equation
For maximum values, when y=5

I got x = [4npi+(-1)^n(2pi) +pi]/12 Mr F says: Wrong. You require ${\color{red} 3x - \frac{\pi}{4} = \frac{\pi}{2} + 2n \pi \Rightarrow x = ....}$.

I would really really appreciate it if someone could check that for me and tell me if it's right or wrong

THankyou =)
..