<span>-a^4-0,8a^6-0,16a^8 = - (a^2+0.4)^2
2) 121m^2-44mn+16n^2. = (11m-4n)^2
3) -a^6+4a^3b-4b^2. =-(a^3-2b)^2
5) 80xy+16x^2+25y^2=(4x+5y)^2
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(a+-b)^2=a^2+-2ab+b^2</span>
Sin²x=1-cos²x=1-4/13=9/13⇒sinx=3/√13
3sin2x=6sinxcosx=6*3/√13 * 2/13=36/13= 2 10/13