Question

solve it by subsitution meathod​

Answer 1

Solution :-

$\sf{7x + 2y = -1}$ ..(1)

$\implies{\sf{7x = -1 - 2y}}$

$\implies{\sf{x = \dfrac{-1 - 2y}{7}}}$ ..(2)

$\sf{3x - 4y = 9}$

$\sf{Substitute\ (2)\ in\ it\ :-}$

$\implies{\sf{3 ( \dfrac{-1 - 2y}{7}) - 4y = 9}}$

$\implies{\sf{ \dfrac{-3 - 6y}{7} - 4y = 9}}$

$\implies{\sf{\dfrac{-3 - 6y - 28y}{7} = 9}}$

$\implies{\sf{-3 - 34y = 9 \times 7}}$

$\implies{\sf{- 34y = 63 + 3}}$

$\implies{\sf{- 34y = 66}}$

$\boxed{\sf{y = \dfrac{-33}{17}}}$ ..(3)

$\sf{Substitute\ (3)\ in\ (1)\ :-}$

$\implies{\sf{7x + 2y = -1}}$

$\implies{\sf{7x + 2 (\dfrac{-33}{17} ) = -1}}$

$\implies{\sf{7x - \dfrac{66}{17} = -1}}$

$\implies{\sf{7x = -1 + \dfrac{66}{17}}}$

$\implies{\sf{7x = \dfrac{-17 + 66}{17}}}$

$\implies{\sf{x = \dfrac{49}{17 \times 7}}}$

$\boxed{\sf{x = \dfrac{7}{17}}}$

So, the value of x & y is :-

$\boxed{\boxed{\sf{y = \dfrac{-33}{17}}}}$

$\boxed{\boxed{\sf{x = \dfrac{7}{17}}}}$

Answer 2

Solution :-

As given

7x + 2y = -1 .....(i)

3x - 4y = 9 ........(ii)

Now we will multiply equation (i) from 2

→ (2)7x + (2)2y = (2)(-1)

→ 14x + 4y = -2 ....(iii)

Now we will add equation (ii) to equation (iii)

$\begin{aligned} 14x + 4y & = -2 \\ 3x - 4y & = 9 \\ \line(1,0){35} & \line(1,0){40} \\ 17x & = 7 \end{aligned}$

So now we have got the Value of

$x = \dfrac{7}{17}$

Now substiting it in equation (ii)

$\rightarrow 3\times \dfrac{7}{17} - 4y = 9 \\\\ \rightarrow \dfrac{21}{17} - 4y = 9 \\\\ \rightarrow 4y = \dfrac{21}{17} - 9 \\\\ \rightarrow 4y = \dfrac{21 - 153}{17}$

$\rightarrow y = \dfrac{-132}{17\times 4} \\ \\ \rightarrow y = \dfrac{-37}{17}$

So

${\huge{\boxed{\sf{x = \dfrac{7}{17}}}}} \\\\ {\huge{\boxed{\sf{y = \dfrac{-37}{17}}}}}$