Respuesta :

calculista
we know that
applying the law of cosines
a² = b²+ c² – 2*b*c*cos(A)

in this problem
a=?
b=20
c=9
A=90°
so
a² = b²+ c² – 2*b*c*cos(A)
but
cos (A)=0
a² = b²+ c²-----> 20²+9²----> a²=400+81----> a²=481-----> a=√481
a=21.93-----> a=22

the answer is
22

B. 22

Law of cosines: a2 = b2 + c2 – 2bccos(A)