Answer:
Option B is correct.
Value of cos(a+B) is,

Explanation:
Using the formula:

Given the values:
and

Using trigonometric identity:

or

or

Find the value of sin a and cos B;
Using trigonometric identity:

=

Similarly;

=

Substitute these given values equation [1] we have;


then;

Since, the angles a and B are in first quadrant angles therefore the value of cos(a+B) is,
