Răspuns:
Explicație pas cu pas:
1. m-mama
f-fiul
m+f=40 ani
m=3*f
3*f+f=40
4f=40 :4
a). f=10ani
b) m+x=2(f +x)
30+x=2(10+x)
30+x=20+2x
x-2x=20-30
-x=-10 :-1
x=10 ani
2. a) Ex=(x+1)^2+2(x-7)+1
Ex=x^2+2x+1+2x-14+1
Ex=(x-2)(x+6)
b) E-1=(-1+1)^2+2(-1-7)+1
E-1=0-16+1
E(-1)=-15
3. a=rad8=2rad2
b=rad2+1/rad2-1(amplificam cu numitorul dar cu semn schimbat)=3+2rad2
2rad2+2/2rad2-2(amplificam la fel)=3+2rad2
8+8rad2+4/4=3+2rad2
12+8rad2/4=3+2rad2
4(3+2rad2)/4=3+2rad2
3+2rad2=3+2rad2
b) a<b
2rad2<3+2rad2(e clar ca 3+2rad 2 e mai mare deoarece se adauga 3)
4.a). ABCD- paralelogram
Pabcd=2AB+2BC=2*30+2*10=60+20=80cm
b). MB=ND=10cm
NC=AM=20cm
DAMN- trapez dreptunghic in D si A
Adamn=(B+b)*h/2=(AM+DN)*DA/2=(20+10)*10/2=150cm^2
MBCN-trapez dreptunghic in C si B
Ambcn=(CN+BM)*BC/2=(20+10)*10/2=150cm^2
Aabcd=L*l=AB*BC=30*10=300cm^2
Rezulta ca: Aabcd=2*A
300=2*150
300=300.
