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[Core] Maths 1980 MC ­øÃÑ

37.­º¥ý¯d·Nªðx^2«Y¥¿©w­t
©OÃD«Y+x^2
-->±øcurve opens upward

§Y«Y¸Ü¥þ±øcurve«Yx-axis¤W­±

¦Ó¯d·NªðÊ\¥»¨­­Ó±ø¥ó«Y>=0
§Y«Y¥i¥H«Y
(1) ±øcurveÀ³¸Ó­nÕi¦í±øx-axis

-->one contact point with x-axis
-->b^2-4ac=0
-->(-k)^2-4(1)(9)=0
-->k^2=36
-->k=+6 or -6


(2) ±øcurve«Yx-axis¤W­±

-->no contact point with x-axis
-->b^2-4ac<0
-->k^2-36<0
-->(k+6)(k-6)<0
-->-6<k<6


±Ncase 1¦P2¦Xªð®I
­Ócondition´N«Y-6<=k<=+6


Answer: C
   
6“5**
http://lsforum.net/board/viewthread.php?tid=273337

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[ÁôÂÃ]
²Ä45ÃD§AûH°ÝÃD«Y
ÂI¸Ñsin(270-a)=-cos a
©O­ÓÀ³¸Ó«Y¤¤¥|trigonometry¤T¨¤¾Ç·|±Ð¨ì
¥ç«Y³Ì°ò¥»
°µ©OºØÂà´«Ú»2¼Ë³¥


(1) sin¤J­±­Ó¼Æ¦r
0, 180, 360´N­ø·|±NsinÅÜ°µcos
90, 270´N­n±NsinÅÜ°µcos


©O­Ó±¡ªp
270-->sin­nÅÜ°µcos


(2) 270-a «YÃä­Óquadrant
§Ú¦a­ø»Ý­n²zÃD¥Ø¤J­±a>180«×
·Ó·í0<a<90¡]¥ô¦ó±¡ªp³£«YËÝ¡^
©Ò¥H270-a«Yquadrant III
®Ú¾ÚªðASTC©O­Ó¤f³Z
§Y«YT©O°Ï
-->±otan«Y¥¿¼Æ
-->sin«Y­t¼Æ
-->©Ò¥H­n¥[­t¸¹Íqcos


(1) sinÅÜcos
(2) ¥[­t¸¹
-->sin(270-a)=(-cos a)

6“5**
http://lsforum.net/board/viewthread.php?tid=273337

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