3а - 4b a(-1, 2), b(2, -5)

To find the value of 3a - 4b, we need to substitute the given values of a and b into the expression.

Given: a = (-1, 2) b = (2, -5)

Substituting the values into 3a - 4b, we have: 3*(-1, 2) - 4*(2, -5)

Multiplying each component of a by 3 and each component of b by 4, we get: (-3, 6) - (8, -20)

Subtracting the corresponding components, we have: (-3 - 8, 6 - (-20))

Simplifying, we get: (-11, 26)

Therefore, 3a - 4b = (-11, 26).