Chứng minh đẳng thức:
1, \(\dfrac{a\left(x-b\right)\left(x-c\right)}{\left(a-b\right)\left(a-c\right)}+\dfrac{b\left(x-a\right)\left(x-c\right)}{\left(b-a\right)\left(b-c\right)}+\dfrac{c\left(x-a\right)\left(x-b\right)}{\left(c-a\right)\left(c-b\right)}=x\)