We will use the Substitution : root5(y^4-8)=x:5√y4−8=x.
rArr (y^4-8)=x^5 rArr d(y^4-8)=d(x^5), i.e., 4y^3dy=5x^4dx⇒(y4−8)=x5⇒d(y4−8)=d(x5),i.e.,4y3dy=5x4dx.
"Therefore, "I=int(root5(y^4-8))^3(4y^3dy)Therefore, I=∫(5√y4−8)3(4y3dy)
=int(x^3)(5x^4)dx=5intx^7dx=5(x^(7+1)/(7+1))=5/8x^8=∫(x3)(5x4)dx=5∫x7dx=5(x7+17+1)=58x8.
rArr I=5/8(root5(y^4-8))^8+C.⇒I=58(5√y4−8)8+C..