Question

3. Find the product of the real roots of the equation, x2 + 18x + 30 = 21x2 +18x +45

JEE/Engineering Exams

Maths

Solution

173

4.0 (1 ratings)

Let ( x^{2}+18 x+30=z ) ( Rightarrow quad z=2 sqrt{z+15} ) ( Rightarrow quad t^{2}=4(t+15) ) ( Rightarrow quad t^{2}-4 z-60=0 ) ( Rightarrow(t-10)(t+6)=0 ) ( Rightarrow quad t=10,-6 ) ( therefore x^{2}+18 x+30=10 quad ) as ( quad x^{2}+18 x+30=-6 ) ( =5 x^{2}+18 x+20=0 quad ) a ( quad x^{2}+18 x+36=0 ) Pdt ( y times sec t=+20 ) Pat. 9 sorts ( =36 )