partial derivative of cos(xln(y)) with respect to x
⚠ cos(xln(y)) is read as cos(x*ln(y)): use * for multiplication, use ^ for a power
Differentiate with respect to x while holding y constant
Let's perform the differentiation: ∂∂x(cos(x·ln(y)))
We differentiate using: ∂∂x(cos(f)) = -∂∂x(f)·sin(f) (where f = x·ln(y))
ⓘ The derivative of cos(x) is -sin(x): ∂∂x(cos(x·ln(y))) = -∂∂x(x·ln(y))·sin(x·ln(y))
-∂∂x(x·ln(y))·sin(x·ln(y))
ⓘ For differentiation with respect to x, ln(y) is treated as constant. A constant factor stays in front of the derivative, (k*u)' = k*u': ∂∂x(x·ln(y)) = ln(y)·∂∂x(x) = ln(y)·1 = ln(y)
▶Derivative:   -ln(y)·sin(x·ln(y))