Gọi I là giao điểm của đường trung trực của BC với BC .  Nối KC

Ta có tam giác EIC = tam giác EIB ( c.g.c )

=> CE = BE ( hai cạnh tương ứng )

chu vi tam giác AEB = AE + AB + BE = AE + AB + CE ( do BE = CE )

=> chu vi tam giác ABE = AB + AC ( do AE + CE = AC )

tam giác KIB = tam giác KIC ( c.g.c )

=> KB = KC ( hai cạnh tương ứng )

chu vi tam giác AKB = AK + BK + AB = AK + KC + AB ( do BK = CK )

xét tam giác ACK theo bất đẳng thức tam giác ta có

AK + CK > AC 

=> AK + CK + AB > AC + AB

=> chu vi tam giác ABK > chu vi tam giác ABE

thiếu đề hay sao ý

:}

hog bic lm=))

Title: A Guide to Making Your School Greener

Introduction: Welcome to our guide on how to make your school greener! By implementing sustainable practices, you can contribute to a cleaner environment and create a positive impact on the planet. In this guide, we will provide you with practical steps to help you and your school become more eco-friendly.

1. Reduce Paper Usage:
Encourage digital communication: Promote the use of emails, online platforms, and shared documents instead of relying on paper-based communication.
Opt for electronic assignments: Encourage teachers to accept electronic submissions for assignments, reducing the need for printed papers.
Utilize both sides of the paper: Encourage students and staff to print on both sides of the paper whenever possible.
2. Implement Recycling Programs:
Set up recycling stations: Place recycling bins strategically throughout the school to make it convenient for everyone to recycle paper, plastic, glass, and other recyclable materials.
Educate on proper recycling: Provide clear instructions on what can and cannot be recycled, ensuring that everyone understands the recycling process.
3. Conserve Energy:
Turn off lights and electronics: Remind students and staff to switch off lights, computers, and other electronic devices when not in use.
Utilize natural lighting: Make the most of natural light by opening curtains and blinds, reducing the need for artificial lighting during the day.
Upgrade to energy-efficient appliances: Encourage the school administration to invest in energy-efficient appliances and LED lighting, reducing energy consumption.
4. Promote Water Conservation:
Fix leaks and drips: Address any leaks or drips in faucets, toilets, or other water fixtures promptly to prevent wastage.
Encourage shorter showers: Raise awareness about the importance of shorter showers to conserve water and encourage students to be mindful of their water usage.
Collect rainwater: Install rain barrels to collect rainwater for watering school gardens or other non-potable uses.
5. Develop Green Spaces:
Start a school garden: Set up a garden where students can learn about sustainable gardening practices and grow their food.
Plant native trees and plants: Native plants require less water and maintenance, while also providing habitat for local wildlife.
Create green roofs: Implement green roofs or living walls to improve insulation and reduce energy consumption while enhancing the aesthetic appeal of the school.
Conclusion: By following these steps, you can make your school a greener and more sustainable place. Remember, small changes can have a significant impact when everyone in the school community works together towards a greener future. Start implementing these practices today and lead the way in creating a more environmentally conscious school environment.

Bài 1: 

a: AB+AC=75-45=30(cm)

b: AB=(30+4):2=17(cm)

=>AC=13cm

\(S=17\cdot13=221\left(cm^2\right)\)

Bài 2: 

a: BC=67-47=20(cm)

b: \(S=\dfrac{15\cdot20}{2}=15\cdot10=150\left(cm^2\right)\)

Chu vi của tam giác ABC là 21cm \(\Rightarrow AB+AC+BC=21 \Leftrightarrow BC=21-6-7=8 (cm)\)

\(\Rightarrow BC>AC>AB\)

\(\Rightarrow \hat{A} > \hat{B} > \hat{C}\) (Quan hệ giữa góc và cạnh đối diện trong tam giác).

Chu vi của tam giác ABC là 21cm 

⇒^A>^B>^C⇒A^>B^>C^ (Quan hệ giữa góc và cạnh đối diện trong tam giác).

chu vi tam giác ABC là

( 3 x 4 ) : 2 = 6 cm2

AC k phải BC

-△ABC∼△HBA (g-g) \(\Rightarrow\dfrac{P_{ABC}}{P_{HBA}}=\dfrac{BC}{BA}=\dfrac{20}{12}=\dfrac{5}{3}\Rightarrow\dfrac{AB}{BC}=\dfrac{3}{5}\) 

\(\Rightarrow AB=\dfrac{3}{5}BC\)

-△ABC vuông tại A có: \(AB^2+AC^2=BC^2\Rightarrow\dfrac{9}{25}BC^2+AC^2=BC^2\Rightarrow AC^2=\dfrac{16}{25}BC^2\Rightarrow AC=\dfrac{4}{5}BC\)

-△ABC∼△HAC (g-g)  \(\Rightarrow\dfrac{P_{ABC}}{P_{HAC}}=\dfrac{BC}{AC}=\dfrac{BC}{\dfrac{4}{5}BC}=\dfrac{5}{4}\Rightarrow\dfrac{20}{P_{HAC}}=\dfrac{5}{4}\Rightarrow P_{HAC}=\dfrac{20.4}{5}=16\left(cm\right)\)