In Problems 21-26, solve the initial value problem.
21. $(1/x + 2y^2x) dx + (2yx^2 - \cos y) dy = 0$,
y(1) $= \pi$
22. $(ye^{xy} - 1/y) dx + (xe^{xy} + x/y^2) dy = 0$,
y(1) = 1
23. $(e^ty + te^ty) dt + (te^t + 2) dy = 0$,
y(0) = -1
24. $(e^tx + 1) dt + (e^t - 1) dx = 0$,
x(1) = 1
25. $(y^2 \sin x) dx + (1/x - y/x) dy = 0$,
y($\pi$) = 1
26. $(\tan y - 2) dx + (x \sec^2y + 1/y) dy = 0$,
y(0) = 1
