Solve 16x² - 81 = 0

The first thing we see is that both coefficients are perfect squares

so the fastest way to get the right answer is to solve this algebraically

16x² = 81

x² =

81 / 16

x = ±√

81 / 16

x = ±

9 / 4

x₁ =

9 / 4

squared andsquared x₂ = -

9 / 4