Which describes the transformation from f(x) = x² to g(x) = 3x²?
A Vertical stretch by a factor of 3
B Vertical compression by 3
C Horizontal stretch by 3
D Reflection across the x-axis
Explanation
A coefficient |a| > 1 outside the function stretches vertically; |a| < 1 compresses. 3x² is narrower (stretched).