Verified answer

(-0.15t²+0.1215) / (t²+0.81)² = 0

(-0.15t²+0.1215) = 0 (by multiplying both sides by (t²+0.81)²

0.15t² = 0.1215

t² = 0.81

t = 0.9 or -0.9

The denominator does not equal 0 with either choice so we are okay.

simple, the whole bottom line dissapears. multiplication of 0 is always 0

rewrite it as: -0.15t²+0.1215 = 0

You can do it how the person above me has done it or alternatively you can solve it by factorisation.

-0.15 ( t² - 0.81) = 0

t² - 0.81 = 0

t² = 0.81

t = ± √0.81

t = ± 0.9

----> -0.15t²+0.1215 = 0----->t = 0.9 or -0.9