Question

Find the value of k, if x=−1 and y=2 is a solution of the equation 4x−ky=10.​

Answer 1

Given:

• 4x - ky = 10⠀⠀⠀⠀⠀⠀⠀⠀ ❬ eq (1) ❭
• x = -1 ⠀⠀⠀⠀⠀⠀⠀⠀ ❬ eq (2) ❭
• y = 2⠀⠀⠀⠀⠀⠀⠀⠀ ❬ eq (3) ❭

Need to find:

• The value of k ?

Solution:

Substituting equation (2) and (3) in (1) , we get ;

➜ 4 (-1) - k (-2) = 10

➜ -4k -2k = 10

➜ 2k = -10 - 4

➜ 2k = -14

➜ k = -14/2

➜ k = -7

Therefore, The value of k is -7.

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Answer 2

Given

• x=-1
• y=2
• x and y are the solution of equation 4x-ky=10

To Find

• Value of k

Solution

We have x and y which are the solution of equation 4x-ky=10

So we put the value in the equation and find k directly

Here,

• x=-1
• y=2

Putting values

$\rm \: 4 \times - 1 - k \times 2 = 10 \\ \\ \rm \implies \: - 4 - 2k = 10$

After this we can do this by two methods

First taking common

$\rm \: -2 (2 + k) = 10 \\ \\ \implies \rm \: 2 + k = - 5 \\ \\ \implies \rm \boxed{ \bf \: k = - 7}$

Method 2

By simplify the equation

$\rm - 4 - 2k = 10 \\ \\ \implies \rm \: - 2k = 10 + 4 \\ \\ \implies \rm \: k = \frac{14}{ - 2} \: \: \: \: \: \: \: \: \: \: \:\\ \\ \implies \boxed{ \bf \: k = - 7} \: \: \: \: \: \: \: \:$

Both the methods are simple to do

By the two methods you can also check your answer