Find a2+b2+c2; if a+b+c=9 and ab+bc+ca=24
a+b+c=9⇒(a+b+c)2=(9)2⇒a2+b2+c2+2ab+2bc+2ca=81⇒a2+b2+c2+2(ab+bc+ca)=81⇒a2+b2+c2+2×24=81⇒a2+b2+c2+48=81⇒a2+b2+c2=81−48⇒a2+b2+c2=33.