Multivariate Calculus 10B, Problem 1

Calculate the following integrals

a) $\int _{0}^{1}\int _{y}^{1}e^{\frac {y}{x}}~dxdy$

b) $\int _{0}^{1}\int _{0}^{cos^{-1}(y)}e^{2x-y}~dxdy$

solution(a):

Here we change order of integration, $\int _{0}^{1}\int _{0}^{x}e^{\frac {y}{x}}~dydx=\int _{0}^{1}[xe^{\frac {y}{x}}|_{y=0}^{y=x}]~dx=\int _{0}^{1}x(e-1)~dx={\frac {1}{2}}x^{2}|_{0}^{1}(e-1)={\frac {1}{2}}(e-1)$ solution(b): Here we change order of integration, Failed to parse (syntax error): {\displaystyle \int _0^{\frac{\pi}{2}} \int_0^{cos(x)} e^{2x - y}~dydx = \int _0^{\frac{\pi}{2}[-e^{2x -y}|_{y = 0}^{y = cos(x)}]~dx = \int_0^1 x(e - 1)~dx = \frac{1}{2}x^2|_0^1(e - 1) = \frac{1}{2}(e - 1)}