Answer:
112 degrees.
Step-by-step explanation:
2*10*8*cos [tex]\alpha[/tex]= [tex]8^{2} +10^{2} -15^{2} = 64+100-225= 164-225=-61[/tex]
now, dividing both sides by 2*10*8,
cos [tex]\alpha[/tex] = -61/160
[tex]\alpha[/tex] = 112.4 degrees = 112 ( appox) ( use calculator for this cos inverse function)