Question

resolva as equações:
 (x-4)²=81

Answer 1

$(x-4)^{2} =81</strong> \\ x^{2} -8x+16=81 \\ x^{2} -8x+16-81 \\<strong><u> x^{2} -8x-65=0$
a=1; b=-8; c=-65
Δ=b²-4ac⇒ Δ=(-8)²-4.1.(-65)⇒ Δ=64+260⇒ Δ=324
x=-b±√∆ / 2.a⇒ x=-(-8)± √324 / 2.1⇒ x=8±18 / 2
x'=8-18 / 2⇒ x'=26 / 2⇒ x'=13
x"=8-18 / 2⇒ x"=-10 / 2⇒ x"=-5
S={-5 , 13}