Question

Work out the value of X.

Answer 1

• 
  `x = 20 {}^ \circ`

Explanation:

That are supplementary, means:

They add up to 180°.

Here is the same case.

Given angles are:

• 4x & 5x

Solved:

• 
  `4x + 5x = 180 {}^ \circ`

Combining them,

• 
  `9x = 180 {}^( \circ)`

Transposing 9 to RHS,

• 
  `x = \cfrac{ \cancel{180} \: {}^(20) }{ \cancel9}`

• 
  `x = 20`

Hence, value of x is 20.

Answer 2

Those are supplementary angles, therefore:

`4x+5x=180\\9x=180\\x=20`