Answer:

Resultant amplitude = 1 unit.

Explanation:

The amplitude of a wave is its maximum displacement during propagation.

Since the two waves are out of phase, the resultant amplitude can be determine by;

Resultant amplitude, [tex]A_{R}[/tex] = [tex]\sqrt{A_{1} ^{2} + A_{2} ^{2} + 2A_{1} A_{2}cos \alpha }[/tex]

                                        = [tex]\sqrt{(A_{1} – A_{2} )^{2} }[/tex]

                                        = [tex]A_{1}[/tex] –  [tex]A_{2}[/tex]

where [tex]\alpha[/tex] is the phase difference.

Given that: [tex]A_{1}[/tex] = 75 units, [tex]A_{2}[/tex] = 74 units, so that;

[tex]A_{R}[/tex] = 75 – 74

     = 1

The resultant amplitude of the two wave when out of phase is 1 unit.