a)3/5=x/10 x×5=30 x=6
b)7/x=21/15 7/x=7/5 x=5
c)x+2/x+7=3x+6/48 (x+7)(3x+6)=(x+2)48 3x²+6x+21x+42=48x+96 3x²+27x-48x-96+42=0 3x²-21x-54=0 a=3,b=-21,c=-54
coeficientul=(-21)²-4x3×(-54)=441+648=1089
x1,2=-b±radical(coeficient)/2a x1,2=-(-21)±radical1089/2×3 x1,2=21±33/6
x1=21-33/6 x1=-12/6 x1=-2
x2=21+33/6 x2=54/6 x2=9
