Why is the amplitude of the radio wave in figure 1 varied?

This is an example of amplitude modulation which is a method to transmit analog signals via radio-spectrum waves. A carrier sine wave (in the image, the one with the higher frequency) is modulated (in amplitude) by another signal (the target of transmission). The carrier due to its appropriate frequency enables successful transmission of a signal that would otherwise be difficult to transmit (due to its too low frequencies) and also enables transmission of multiple channels at different carrier frequencies.

Classic example: AM radio.

0 = 0.40 / 0 = 0

= 0.20 = 9.80 ⁄2 =?

=0 , = = 0.20 =0.50 0 0.40 ⁄

=0−122 =0−12(9.80 ⁄2)(0.50)2 =1.2