Răspunsuri

2014-08-25T15:49:09+03:00
L: L   dp cu 2,7

l/2= L/7=k

l=2k
L=7k

P=2l+2L
P=180

2*2k+2*7k=180
4k+14k=180
18k=180
k=10

l=2*10=20cm
L=7*10=70cm

A=L*l= 20*70= 1400 cm^2
2014-08-25T15:58:40+03:00
Notez cu L = latura mare si l = latura mica
Perimetrul = 2 x (L+l)=180

 \frac{l}{2} = \frac{L}{7}

de aici il scot pe l ca fiind :
7 * l = 2 * L
l =  \frac{2 * L}{7}

acum inlocuiesc in suma:

 \frac{2 * L}{7} + L = 180: 2 = 90

aduc la acelasi numitor

 \frac{2 * L + 7 * L}{7} = 90

9 * L = 90 * 7
9 * L = 90* 7 
L = 90 * 7 : 9 = 10 * 7 = 70

l =  \frac{2 * L}{7} = 2 *  70 : 7 = 2 * 10 = 20
Aria = l * L = 70 * 20 = 1400