I have done part a and b, but need help with part c.A) show that $\displaystyle y = 6sin2x + 4cos2x $ satisfies the equation

$\displaystyle \frac{d^{2}y}{dx^{2}} +4y = 0 $

b)the expression $\displaystyle y = 6sin2x + 4cos2x $ can be written as $\displaystyle R sin(2x + a) $ where R and α are positive constants,

0 < α < pi/2. Find the values of R and α, correct to 3 decimal places.

(c) What is the smallest positive value of x where y has a point of inflection?

$\displaystyle \sqrt{52}sin(2x + 0.588) $

$\displaystyle \frac{d^{2}y}{dx^{2}} = -24sin2x - 16cos2x $

Thank you.