Expand using suitable identity: ${\left(-2x+5y-3z\right)}^2$

Simplify $\frac{81x^2-49y^2}{9x+7y}$

If $a+b+c=13$ and $ab+bc+ca=54$, then $a^3+b^3+c^3-3abc$ is equal to:

What is the simplified value of: $\frac{{\sin }^3 {21}^{\circ }+{\cos }^3 {19}^{\circ }}{\sin {21}^{\circ }+\cos {19}^{\circ }}+{\sin }^2 {69}^{\circ }+{\cos }^2 {71}^{\circ }+\frac{1}{\sec {69}^{\circ }\mathrm{cosec} {71}^{\circ }}$ is

What is the simplified value of $\frac{(2.7{)}^3+(1.3{)}^3}{(2.7{)}^2-2.7\times 1.3+(1.3{)}^2}?$

Expand : ${\left(\mathrm{W}-9\right)}^2$

1. $\left({\mathrm{W}}^2-9\mathrm{W}+81\right)$

2. $\left({\mathrm{w}}^2-9\mathrm{W}+18\right)$

3. $\left({\mathrm{W}}^2-18\mathrm{W}+81\right)$

4. $\left({\mathrm{W}}^2-18\mathrm{W}-81\right)$