10)
3(x+5)-5(1-x)(1+x)=(x+3)²+(2x-1)²+13
3x+15-5+5x²=x²+6x+9+4x²-4x+1+13
3x+10=2x+23
x=13
11).a=4√5(5/4√5+√5/10)-(2√6/7+6/√6-√6)×7/√6=
=5+20/10-(2+7-7)=5+2-2=5
12.
x=pret initial
x-10 lei=pret dupa prima ieftinire
x-10-(x-10)×20%=x-10-x/5-2=4x/5-8 =pret dupa a 2-a ieftinire
4x/5-8=x/130%
4x/5-8=10x/13
52x-520=50x
2x=520
x=260 lei pret initial
verificare
260-10=250 lei
250 lei×20%=50
250-50=200 lei pret final
200×130%=260 lei pret initial
13.
∡ACB=45°
triunghiul ADC este dreptunghic isoscel rezulta ca AD=DC=12 cm
AC=√(12²+12²)=12√2
∡ABC=180°-(105°+45°)=30°
deci tg 30°= 12/BD=1/√3 BD=12√3
BC=BD+DC=12√3+12
A=(12√3+12)×12/2=(12√3+12)×6=72√3+72
AB=√(12²+12√3²)=√(144+432)=√576=24
P=12√2+12+12√3+24=12√2+12√3+36=12(√2+√3+3)
