120
|a+b|=√(a²+b²+2abcos|a-b|=√(a²+b²-2abcosa²+b²+2abcos2abcos<(ab)=-2abcos<(ab)<br>cos<(ab)=-cos<(ab)<br>2cos<(ab)=0<br>cos,(ab)=0
<(ab)=90⇒a_|_b<br>121
p=a+2b q=2a+b
p*q=(a+2b)(2a+b)=2a²+ab+4ab+2b²=2|a|²+2|b|²+5|a|*|b|*cos90=4|a|²
|p|=√(a+2b)²=√(|a|²+4*|a|*|b|*cos90+4|b|²)=|a|*√5
|q|=√(2a+b)²=√(4|a|²+4*|a|*|b|*cos90+|b|²)=|a|*√5
cos<(pq)=pq/(|p|*|q|)=4|a|²/(|a|√√5)²=4/5=0,8<br>