Question

If x+2y=9and xy=7,find the value ofx2+4y

Answer 1

$heya....... \\ given.... \\ x + 2y = 9....eqn \: 1 \\ xy = 7 = > y = \frac{7}{x} ....eqn \: 2 \\ from \: eqns \: 1and \: 2 \\ x + 2 \times \frac{7}{x} = 9 \\ x {}^{2} + 14 = 9x \\ x {}^{2} - 9x + 14 = 0 \\ x {}^{2} - 7x - 2x + 14 = 0 \\ x(x - 7) - 2(x - 7) = 0 \\ (x - 7)(x - 2) = 0 \\ x = 2 \: and \: 7 \\ then....y = \frac{7}{2} \: if \: x = 2 \\ y = \frac{7}{7} = 1 \: if \: x = 7 \\ finding \: the \: value \: given..... \\ x {}^{2} + 4y \\ we \: r \: taking \: x = 2 \: andy = \frac{7}{2} \\ = 2 {}^{2} + 4 \times \frac{7}{2} \\ = 4 + 14 = 18. \\ \: \: hope \: it \: helps \: u \: dear....$