A multiplicative inverse of an integer a is an integer x such that the product ax is congruent to 1 with respect to the modulus m.
1. 
Check:
The multiplicative inverse of 5 in
is 9.
2. 
Check:
The multiplicative inverse of 5 in
is 5.
3. 
Check:
The multiplicative inverse of 5 in
is 8.
Answer:
It is the 2nd option
Step-by-step explanation:
Use the the double angle formula:
sin(2A)=2sin(A)cos(A)
substitute 2x for A, then
20sin(2x)cos(2x)=10(sin(2(2x))cos(2(2x))=10sin(4x)
I would say A is the only logical answer