Question

aflati numarul natural a din proportiile: 3/7=a/28
a/2=7/3,5
4/a=a/9
0,6/2•a= 0,9/21​

Answer 1

Pentru a putea afla o necunoscuta dintr-o proportie trebuie sa egalam produsul mezilor cu produsul extremilor:

$\frac{x}{y} =\frac{z}{v} \\\\x\cdot v=y\cdot z$

Produsul celor doua diagonale se egaleaza

a)

$\frac{3}{7} =\frac{a}{28} \\\\7=28\cdot 3\\\\a=\frac{28\cdot 3}{7}=12$

b)

$\frac{a}{2} =\frac{7}{3,5} \\\\3,5a=7\cdot 2\\\\a=\frac{7\cdot 2}{3,5}=4$

c)

$\frac{4}{a} =\frac{a}{9} \\\\4\cdot 9=a^2\\\\36=a^2\\\\a=6$

d)

$\frac{0,6}{2a}=\frac{0,9}{21} \\\\2a\cdot 0,9=21\cdot 0,6\ \ \ |:2\\\\a\cdot 0,9=21\cdot 0,3\ \ \ \ |:0,33a=21\\\\a=7$

Un alt exercitiu gasesti aici: https://brainly.ro/tema/132640

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