log x is defined only when x > 0 Now, the 3rd term in the expansion T2+1=‌5C2.x5−2.(xlog10x)2=1,000,000 (given) ⇒x3+2log10x=105 Taking logarithm of both sides, we get (3+2log10x).log10x=5 ⇒ 2y2+3y−5=0 where log10x=y ⇒ (y−1)(2y+5)=0 ⇒ y=1 or −