If $\vec{x}and\vec{y}$ are two non-collinear vectors and $ABC$ isa triangle with side lengths $a,b,andc$ satisfying $\left(20a-15b\right)\vec{x}+\left(15b-12c\right)\vec{y}+\left(12c-20a\right)\left(\vec{\times }x\vec{y}\right)=0,$ then triangle $ABC$ is a. an acute-angled triangle b. an obtuse-angled triangle c. a right-angled triangle d. an isosceles triangle

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