Answer:
D
Step-by-step explanation:
If x° and y° are complementary angles, then x°+y°=90° and
[tex]\sin x^{\circ}=\cos y^{\circ} \ [\text{Cofunctions rule}][/tex]
Check all options:
A. 18°+72°=90°, so
[tex]\sin 18^{\circ}=\cos 72^{\circ}\ [\text{true}][/tex]
B. 55°+55°=110°, these angles are not complementary and
[tex]\sin 55^{\circ}\neq\cos 55^{\circ}\ [\text{false}][/tex]
C. 72°+18°=90°, so
[tex]\sin 72^{\circ}=\cos 18^{\circ}\ [\text{true}][/tex]
D. Both A and C are true.
