: Đẳng thức nào sau đây đúng ?
A. cos4x – sin4x = 2-cos2x B. cos4x – sin4x = 1+2sin2x

Step-by-step explanation:

A. cos4x-sin4x=2-cos2x

option 1 is correct.

step-by-step explanation:

y varies inversely with x and constant of variation is 4

the equation will be:

y = k/x

where k =4 so,

y = 4/x

if we put values of x of option 1 in the above equation and find values of y

y = 4/-2 => y =-2

y = 4/-1 => y = -4

y = 4/1 => y = 4

y = 4/2 => y =2

so, all the values of x and y are correct.

if we put values of x given in other options and find value of y we cannot find whole table satisfying the equation.

hence option 1 is correct.

5

step-by-step explanation: