Ta có: `hatA + hatB + hatC + hatD = 360^o`

`-> 10x = 360^o`

`-> x = 36^o`.

`-> 4x = 144^o`

`-> 4x + x = hatB + hatD = 180^o`

`-> AB //// CD.`

`a, -> x in ƯC(120, 240, 300)`

`-> x in Ư(60)`.

Mà `x >=10`

`-> x = 10, 20, 30, 60.`

`b, ->x in BC(16, 15, 11)`

`-> x in B(2640).`

`-> x in {0, 2640, 5280, ...}`

mà `x < 3000`.

`-> x  = 0, 2640`.

`a, -> x = (3/4)^2 = 9/16`

`b, -> x = +-5/8`

`c, -> x = 81`

`d, -> x = 5^2 = 25`

`e, -> x^2 = 64 -> x = +-8`

`f, sqrt(x+1) = 2 -> x + 1 = 4 -> x = 3`

`g, -> x + 1 = 4/9 -> x = -5/9`

`h, -> (5+x)^2 = 4`

`->` \(\left[{}\begin{matrix}5+x=2\\5+x=-2\end{matrix}\right.\)

`->` \(\left[{}\begin{matrix}x=3\\x=-7\end{matrix}\right.\)

`a, B(x) = x^4 - x^2 - [2x^3 -(x^2+1)]`

`= x^4 - x^2 - 2x^3 + x^2 - 1`

`= x^4 - 2x^3+ 1`

Bậc là `4`.

Hệ số cao nhất là `1`

Hệ số tự do là `1`