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D( x )
49-x^2 = 0
4-(2*x) = 0
3/(49-x^2) = 0
49-x^2 = 0
49-x^2 = 0
-1*x^2 = -49 // : -1
x^2 = 49
x^2 = 49 // ^ 1/2
abs(x) = 7
x = 7 or x = -7
4-(2*x) = 0
4-(2*x) = 0
4-2*x = 0
4-2*x = 0 // - 4
-2*x = -4 // : -2
x = -4/(-2)
x = 2
3/(49-x^2) = 0
3/(49-x^2) = 0
3 = 0
x belongs to the empty set
x in (-oo:-7) U (-7:2) U (2:7) U (7:+oo)
((21*x)/(4-(2*x)))/(3/(49-x^2)) = 0
((21*x)/(4-2*x))/(3/(49-x^2)) = 0
(21*x*(49-x^2))/(3*(4-2*x)) = 0
( 21*x )
21*x = 0 // : 21
x = 0
( 49-x^2 )
-1*x^2 = -49 // : -1
x^2 = 49
x^2 = 49 // ^ 1/2
abs(x) = 7
x = 7 or x = -7
x in { 7}
x in { -7}
x = 0
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