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Математика 5 - 9 классы
13.12.2019 18:05
Дан ромб ABCD, точка O пересечения диагоналей AC и BD, короткая диагональ равна стороне ромба.
1) Угол между векторами BA−→ и BD−→− равен °;
2) угол между векторами CB−→− и DA−→− равен °;
3) угол между векторами AB−→ и CA−→− равен °;
4) угол между векторами AD−→− и DB−→− равен °;
5) угол между векторами OB−→− и OC−→− равен
1.danced, opened, took , rained, had , washed, did ,watched ,cleaned ,went, made , was , got ,lived , wrote
2.we didn't go to Moscow last summer.
the children didn't have dinner at 2o'clock yesterday.
they didn't watch film last week/
I didn't get up at 8 o'clock yesterday.
it didn't rain two days ago
Ann didn't live in S.Petersburg last year/
She didn't read an untersting book the day before yesterday.
I didn't my homework after school yesterday.
3.where the children play in the garden yesterday?
did Tom write a latter three days ago&
What father cook dinneh yesterday&
Who mother go to work by bus yesterday?
When we have a bath the day before yesterday?
Why Nick come home in the aafternoon?
What grandmother make tea in the morning?
4.1 We didn't have lunch at 1o'clock yesterday.Did we have lunch at 1o'clock yesterday? where we have lunch at 1 o'clock yesterday? Who have lunch at 1 o'clock yesterday?
4.2 It didn't show last week.Did it show last week? Where it show last week? Who ishow last week?
5/1 I halped the mom yesterday.
5/2 where you live last month?
5/3 Did they wake up at 7 am ?
5/4 We didn't go to school yesterday
5/5Who watch the TV on Sunday ?
∠С=60°. СД - биссектриса и делит его на 2 угла по 30°.
Сумма острых углов прямоугольного треугольника равна 90°. ⇒
В ∆ АВС ∠ А=90°-60°=30°
В ∆ АДС ∠САД= ∠АСД=30°. Равенство углов при одной из сторон - признак равнобедренного треугольника. Следовательно, АД=ДС.
∆ ВСД - прямоугольный, катет ВД противолежит углу 30° и равен половине гипотенузы СД (свойство).
Следовательно, СД=2ВД=10 см
Катет АВ=СД=10 см.
АВ=ВД+АД=5+10=15 см
Объяснение: