Question

Which of the following functions has a maximum y value of 4?

y = 4cosx
y = cos4x
y = cosx + 4
y = cos(x + 4)

Answer 1

the answer is y = 4cosx

Answer 2

y = 4cosx

Explanation:

Since we have cosx lying between -1 and 1, we have

y =4cosx lying between 4(-1) and 4(1)

i.e. maximum value is 4.

II option is incorrect because cos4x has maximum value only as 1.

III option is also incorrect because cos(x)+4 has maximum as 1+4=5

IV option is also incorrect because cos(x+4) has maximum as 1

As a result we have out of 4 options given only I option satisfies the condition that the function has a maximum value of 4.