sin^2(a) + cos^2(a) = 1(-0.1)^2 + cos^2(a) = 10.01 + cos^2(a) = 1cos^2(a) = 0.99
cos(a) = ±√0.99cos(a) = ±0.994987
-13cos(2a) = -13(0.994987)^2-13cos(2a) = -13(0.989990060169)-13cos(2a) = -12.8688707822
Therefore, the value of -13cos(2a) when sin(a) = -0.1 is approximately -12.8689.
sin^2(a) + cos^2(a) = 1
(-0.1)^2 + cos^2(a) = 1
0.01 + cos^2(a) = 1
cos^2(a) = 0.99
cos(a) = ±√0.99
cos(a) = ±0.994987
-13cos(2a) = -13(0.994987)^2
-13cos(2a) = -13(0.989990060169)
-13cos(2a) = -12.8688707822
Therefore, the value of -13cos(2a) when sin(a) = -0.1 is approximately -12.8689.