Do NOT use the quotient rule (though it will work). This is a Power Rule problem: y = −2x−3. Reserve the Quotient Rule for situations in which there are variables in BOTH the numerator and the denominator.
This is not technically a Chain Rule problem, though you may use it.
This calls for the Quotient Rule.
Product Rule & Chain Rule combined.
Refer to the hint in part (a). And recall that the reciprocal of cosx is secx.