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Hi there! Have questions about your homework? At Brainly, there are 60 million students who want to help each other learn. Questions are usually answered in less than 10 minutes. Try it for yourself by posting a question! :D

Sec=1/cos tan=sin/cos so,....by using (a-b)²=a²-2ab+b², we get, (1/c²)-(2/c)+1-(s²/c²)+2s²/c-(s²) i have bolded,some terms in specific manner....we will work on them... by pythagoras' identity, sin²+cos² = 1 so....we wll get, =2+2cos-sin² =1+1+2cos-sin² =cos²-2cos+1 =(1-cos)²...........proved