21. \( \left(4-x^{2}\right) \sqrt{-1-3 x}=0 \)

What should be, subtracted from \( 8 x-3 y+4 \) to get \( 3 x-2 y+4 \).

\( 8 x y \) is a monomial expression. Is the statement true or fause?

The cost price of a pen is Rs \( (3 x+5) \) and is selling price is \( \operatorname{Rs}(4 x+3) \) Write the formulato find protit.

\( 1<\quad \begin{array}{r}\text { Determine whether the ordered pair }(4,5) \text { is a solution of the system. } \\ \begin{array}{r}3 x+2 y=2 \\ 2 x+y=3\end{array}\end{array} \)

\( 1 \leftarrow \begin{array}{l}\text { Determine whether the ordered pair }(2,6) \text { is a solution of the system. } \\ \begin{array}{l}x+y=8 \\ x-y\end{array}\end{array} \)