If 10 times the tenth term of an A.P is equal to 30 times the thirtieth term, then find its 40th term.
0
10×t10=30×t30
10×[a+(9−1)d]=30×[a+(30−1)d]
10×(a+8d)=30×(a+29d)
(10a+80d)=(30a+870d)
−20a=790d
−10a=390d
10a+390d=0
a+39d=0 = 40th term = 0