Question

5. If 4x - 9 =10 and xy = -1, then find the value of 16x2 +81 y2​

Answer 1

Answer:

$4x - 9 = 10 \\ 4x = 10 + 9 \\ 4x = 19 \\ x = \frac{19}{4}$

$xy = - 1 \\ ( \frac{19}{4} )y = - 1 \\ y = \frac{ - 4}{19}$

$= 16 {x}^{2} + 81 {y}^{2} \\ = 16( \frac{19}{4} {)}^{2} + 81( \frac{ - 4}{19} {)}^{2} \\ = 16 \times \frac{361}{16} + 81 \times \frac{16}{361} \\ = 361 + 3.6 \\ = 367.6$