Mathematics for IGCSE & O level - Proportion (Section 1 - No. 47)
If *y* is directly proportional to *x* and *z*, which equation expresses the relationship, where k is a constant?
y = kx + z
y = kxz
y = k(x+z)
x = kyz
Giải thích
Directly proportional to x and z implies y = kxz