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b)7x-4/x=(-2/3)³
3.Efectuează: [(1/2)la puterea 100-(1/2)la puterea 99+(1/2)la puterea 98]:0,75
4. Trei nr sunt direct proporționate cu 1/2;1/3;1/4
a)Daca suma nr este 13 aflați cele 3 nr
b) care sunt nr,daca media aritmetica este 8,(6)?

Răspuns :

Renatemambouko
b)(7x-4)/x=(-2/3)³
(7x-4)/x=-8/27
189x-108=-8x
197x=108
x=108/197

 3.[(1/2)¹⁰⁰-(1/2)⁹⁹+(1/2)⁹⁸]:0,75=
=(1/2)⁹⁸×[(1/2)²-(1/2)¹+(1/2)⁰]:75/100=
=(1/2)⁹⁸×(1/4-1/2+1) × 4/3=
=(1/2)⁹⁸(1-2+4)/4 × 4/3=
=(1/2)⁹⁸ ×3/4 × 4/3=
=(1/2)⁹⁸

 4. a/(1/2)=b/(1/3)=c/(1/4)    2a=3b=4c       b=2a/3    c=2a/4=a/2
a) a+b+c=13     a+2a/3+a/2=13   6a+4a+3a=78   13a=78   a=6
                                                                                              b=2*6/3=4
                                                                                              c=6/2=3


b)8,(6)=(86-8)/9=78/9=26/3
a) (a+b+c)/3=26/3   a+b+c=26      a+2a/3+a/2=26     6a+4a+3a=156   13a=156   a=12           b=2*12/3=8        c=12/2=6