Question

find the sum of the following arithmatic progression 21+22+...51​

Answer 1

$\huge\displaystyle \sf \red{\int \limits^{ \frac{ \pi}{2} }_{0} \frac{3 \sqrt{ \cos \theta} }{( \sqrt{cos \theta} + \sqrt{sin \: \theta}) {}^{5} } \: d \theta}$