Cau 41: B

sin30=1/2

Cau 42: 

$x1^{4}$ +$x2^{4}$ =(x1²+x2²)²-2(x1x2)² = [(x1+x2)²-2x1x2]²-2(x1x2)² 

Cau 43: A

Goi a, b, c lan luot la so ngay lam viec cua 3 may

=> a/3 = b/4= c/ 5 (1)

Goi x, y, z lan luot la so gio lam viec cua 3 may

=> x/6= y/7= z/8 (2)

Goi m, n, p lan luot la so cong suat cua 3 may.

=> 5m= 4 n= 3p <=> m/1/5 = n/1/4=  p/1/3 (3)

Ma axm + byn + czp= 359 (4)

Tu (1); (2); (3); (4) => axm/18/5 = byn/ 7 = czp/40/ 3 = 359/359/15= 15

=> axm=54; byn=105; czp=200

Vay may xay duoc it nhat la 54 tan

Cau44: C

y=x-4 cat Oxy tai 2 diem A(4;0) va B(0;-4) nen OP min = duong cao ha tu O xuong AB

Cau 45: C

Ta phan tich : 1/5²=1/5.5 < 1/4.5 (1/25<1/20) tuong tu 1/6²<1/5.6 

ma 1/4.5 = 1/4-1/5 ; 1/5.6=1/5-1/6 ....

Vay S<1/4-1/100=24/100 hay S<1/4

Cau 46: A

Moi so hang cua S deu co so mu la 4n+1 nen se giu nguyen chu so tan cung. vay chu so tan cung cua S=2+3+4+....+2022=2045252 

(Tong day so cach deu = (So dau+so cuoi) x so so hang / 2)

Cau 47:D

Goi H la giao diem cua MN va OO' . Ta co the tinh OH va O'H bang pytago cua OMH va O'MH

Cau 48 A

Ke AH⊥BC Ta co goc CAH=60* vi ACB=30*

Tam O duong tron ngoai tiep tam giac la giao diem cua 2 duong trung truc nen O se nam tren AH

Ke duong trung truc Dx tren canh AC cat AH tai O. Xet tam giac DOA vuong tai D ta co cosDAH=DA/AO => 1/2=4/OA =>OA=R=8 ⇒C=2πR=16π

Cau 49 D

Dinh ly Menelaus