kẻ `AH ⊥ BC`
ta có: `sinC=` $\dfrac{AH}{AC}$
`⇒ AH= sin``30^o``. 10= 5`
`⇒ HC=` $\sqrt{AC^2-AH^2}$`=` $\sqrt{10^2-5^2}$`=`` 5`$\sqrt{3}$
`tanB=` $\dfrac{AH}{BH}$
`⇒ BH=` $\dfrac{5}{tan45^o}$`= 5`
`⇒ BC= BH+ HC= 5+ 5`$\sqrt{3}$
`S_{ΔABC}``=` `1/2``. AH. BC=` `1/2``. 5` `(5+ 5`$\sqrt{3}$`)` `=` $\dfrac{25+25\sqrt{3}}{2}$ `≈` `34,25cm²`
🍀 @ɷįᵰƫ 🍀
Đáp án + Giải thích các bước giải:
Kẻ đ/cao AH
`\text{ΔAHC vuông tại H}`
`⇒AH=AC.sin(30^0)=10.1/2=5(cm)`
`⇒HC=AC.cos(30^0)=10.(\sqrt{3})/(2)=5\sqrt{3}(cm)`
`\text{ΔAHB vuông tại H}`
`⇒AH=AB.sin(45^0)`
`⇒AB=(AH)/(sin(45^0))=5/(\sqrt{2}/2)=5\sqrt{2}(cm)`
`⇒HB=AB.cos(45^0)=5\sqrt{2}.(\sqrt{2})/(2)=5(cm)`
`⇒BC=HB+HC=5+5\sqrt{3}≈13,7(cm)`
`⇒S_{ΔABC}=1/2.AH.BC=1/2.5.5+13,7=34,25(cm^2)`
Cho hình thang cân ABCD (AB//CD) có A=B=60( độ), AB = 4,5cm; AD = BC = 2 cm. Tính độ dài đáy CD và diện tích hình thang cân ABCD.
cần giúp gấp pls , 1 bài cũng đc
Cho tam giác ABC nhọn . H là trực tâm tam giác ABC. Gọi M,N,P lần lượt là trung điểm các cạnh AB, BC, AC .Gọi I , J , K lần lượt là trung điểm của đoạn thẳng HA, HB, HC . a) Chứng minh MBkJ là hình chữ nhật . b) Chứng minh MK=IM=JP nhớ lm theo cách lớp 8 nha thank
Giúp mình với!!!!!! Tính giá trị biểu thức: a)A=(x+3)($x^{2}$ -3x+9)-(3-2x)($4x^{2}$ +6x+9) tại x=20 b)B=(2x-y)($4x^{2}$ +2xy+$y^{2}$ )+$2y^{3}$ biết 2x+y=20 c)C=($x+y)^{3}$ +$y^{3}$ biết 2x+y=0
Quy đồng phân thức a, 2/ x^2+2x ; 8-2x/x^2-4 ; 1-2x/ x^3+8 b, x/ x+2 ; 4/ x-2 ; 8x/ 4- x^2 c, x/ x^2+ xy+ xz+yz ; y/ y^2+xy+yz+xz d, 1/ x ²-1 ; 1/ x^4-1; 1/ x^8-1
Giải pt ( khó phết :< chắc các ông là dễ)
Mọi người ơi, giúp mik vs, mik phải nộp bây giờ rồi
Mong mn giúp đỡ ( cảm ơn mn nha ^_^ )
giúp e với e cho 5 sao ngay luôn ạ III. Change each of the following sentences into reported speech. 1.John said, “I want to attend a famous university.” -> John said ________________________________________________ 2. “I’m looking for the book you gave me last week,” Mary said to Peter. -> Mary told Peter_____________________________________________ 3. Janet said to John, “I did not promise to send you a telegram.” -> Janet _____________________________________________________ 4. “I will get myself a drink,” she said. -> She said ___________________________________________________ 5. “I cannot drive them home,” he said. -> He said _____________________________________________________ 6. “Peter, do you prefer tea or coffee?” she said. -> She _______________________________________________________ 7. “The film began at seven o’clock,” he said. -> He said ____________________________________________________ 8. The father said, “I was on a business trip the whole day yesterday.” -> The father ___________________________________________________ 9. “My brother will get married next month,” James said. -> James ______________________________________________________ 10. Henry said to his mother, “Come and spend a week with us.” -> Henry told __________________________________________________ 11. He said to me, “Keep a seat for me in the lecture hall.” -> He _________________________________________________________ 12. Mike said to Henry, “Give me my book back, please.” -> Mike ______________________________________________________ 13. “Don’t play on the grass, boys,” she said. -> She _________________________________________________________ 14. “Don’t make so much noise,” he said. -> He ___________________________________________________________ 15. Jane said to Mary, “Will you be free tomorrow?” -> Jane asked _____________________________________________________
Nguyên tử Natri có 11p,11e,12n. Tinh khối lượng nguyên tử Natri
Loga.vn - Cộng Đồng Luyện Thi Trực Tuyến
