If ΔABC is right angled at C, then the value of cos (A+B) is
It is given that C = 90°
In ABC
A +
B +
C = 180 [
sum of interior angles of a triangle is 180°]
A +
B + 90o = 180 [
C = 90° (given)]
A +
B = 1800 – 900
A +
B = 90° …(1)
cos(A +
B) = cos (90°)
cos(90°) = 0
[ from the table of trigonometric ratios of angles we know that cos 90° = 0]
Hence option A is correct.