For the functions w=5x^2y^2, x=cost, and y=sint, express dw/dt as a function oft, both by using the chain rule and by expressing w in terms of t and differentiating directly with respect to t.

• Find dw/dt
• Find dw/dt at 2pi/3

For the functions w=xy+yz+xz, x=3u+2v, y=3u2v, and z=uv, express w/u and w/v using the chain rule and by expressing w directly in terms of u and v before differentiating.

• Evaluate w/u and w/v at the point (u,v)=1/4,1.