a, (2x - 130) : 4 + 213 = 5² + 19
(2x - 130) : 4 + 213 = 25 + 19
(2x - 130) : 4 + 213 = 44
(2x - 130) : 4 = 44 - 213
(2x - 130) : 4 = -169
2x - 130 = -169 . 4
2x - 130 = -676
2x = -676 + 130
2.x = -546
x = -546 : 2
x = -273
b, (x-6)² =9
(x-6)² = (+3)²
Ttường hợp 1:
x - 6 = 3
x = 3 + 6
x = 9
Trường hợp 2:
x - 6 = -3
x = -3 + 6
x = 3
Vậy x ∈ {3 ; 9}
c, (5² + 3²) . x + (5² - 3²) . x - 40 . x = 10²
x . (5² + 3² + 5² - 3² - 40) = 10²
x . (25 + 9 + 25 - 9 - 40) = 100
x . (34 + 25 - 9 - 40) = 100
x . (59 - 9 - 40) = 100
x . (50 - 40) = 100
x . 10 = 100
x = 100 : 10
x = 10
#Nocopy
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