cos(7π/10)cos(3π/10) - sin(3π/10)sin(7π/10)
Using the trigonometric identity cos(a)cos(b) - sin(a)sin(b) = cos(a + b), we have:
= cos(7π/10 + 3π/10)= cos(10π/10)= cos(π)= -1
Therefore, the value of the given expression is -1.
cos(7π/10)cos(3π/10) - sin(3π/10)sin(7π/10)
Using the trigonometric identity cos(a)cos(b) - sin(a)sin(b) = cos(a + b), we have:
= cos(7π/10 + 3π/10)
= cos(10π/10)
= cos(π)
= -1
Therefore, the value of the given expression is -1.