2) cos* a - sin" a = cos 2 a; 3) ctga sin 2 a = ctga cos 2 a;
4) ctg, -tg, = 2ctga;

люди (((​

х2 – 25 =(x-5)(x+5)

144 – у2 =(12-5y)(12+y)

81 – 4с =(9-2c)(9+2c)

(х-у)2 – 81= (x-y-9)(x-y+9)

121 – 25у2 =(11-5y)(11+5y)

с2 –100=(c-10)(c+10)

49с2 – у2 =(7c-y)(7c+y)

1 – 4с2 =(1-2c)(1+2c)

(х+7)2 – 36 =(x+7-6)(x+7+6)

100 – 64у2 =(10-8y)(10+8y)

100 - 4х2 =(10-2x)(10+2x)

36р2 – 49у2 =(6p-7y)(6p+7y)

х6 – 36с2 =(x3-6c)(x3+6c)

(х-4)2 – (с-5)2 =(x-4-c+5)(x-4+c-5)

1 – 25с2 =(1-5c)(1+5c)

64а2 - х2 =(8a-x)(8a+x)

400р8 – 49у4 =(20p4-7y2)(20p4+7y2)

1 – 36с6 =(1-6c3)(1+6c3)

(х-1)2 – (с-5)2 =(x-1-c+5)(x-1+c-5)

а2 –4с2=(a-2c)(a+2c)

Объяснение:

x2 – 25 = ( x - 5 )( x + 5 )

144 – y2 = ( 12 - 5y )( 12 + y )

81 – 4c = ( 9 - 2c )( 9 + 2c )

( x - y )2 – 81 = ( x - y - 9)( x - y + 9 )

121 – 25y2 = ( 11 - 5y )( 11 + 5y )

с2 – 100 =( c -10 )( c + 10 )

49с2 – у2 = ( 7c - y )( 7c + y )

1 – 4с2 = ( 1 - 2c )( 1 + 2c )

(х+7)2 – 36 =( x + 7 - 6 )( x + 7 + 6 )

100 – 64у2 = ( 10 - 8y )( 10 + 8y )

100 - 4х2 =( 10 - 2x )( 10 + 2x )

36р2 – 49у2 = ( 6p - 7y )( 6p + 7y )

х6 – 36с2 =( x3 - 6c )( x3 + 6c )

(х-4)2 – (с-5)2 = ( x - 4 - c + 5 )( x - 4 + c - 5 )

1 – 25с2 = ( 1 - 5c )( 1 + 5c )

64а2 - х2  = ( 8a - x )( 8a + x )

400р8 – 49у4 = ( 20p4 - 7y2 )( 20p4 + 7y2 )

1 – 36с6 = ( 1 - 6c3 )( 1 + 6c3 )

(х-1)2 – (с-5)2 = ( x - 1 - c + 5 )( x - 1 + c - 5 )

а2 – 4с2 = ( a - 2c )( a + 2c )